Objective:
California leafy vegetables have one or two key herbicides, which could be lost due to high manufacturing and regulatory costs. There is no effective post-emergence herbicide against broad-leaf weeds for lettuce and spinach. It is essential to find dependable and sustainable weed control strategies to prevent crop loss. We propose to develop herbicide-tolerant lettuce and spinach through conventional breeding. It will reduce herbicide use by replacing high rate herbicides with low rate products.

Approach:
In the first year, we will treat lettuce and spinach seeds with ethyl methane sulfonate to generate new germplasm. Treated seeds will be planted to produce progeny for screening with glyphosate (Roundup) herbicide. We will also screen spinach germplasm for tolerance to linuron, prometryn and bentazon herbicides, as varietal differences in tolerance have been reported. Putative tolerant lines will be tested in the second year to confirm the results. We will also start to study the inheritance of the trait. If only partial tolerance is found, these plants will be crossed to each other to increase the level of tolerance. If the tolerance exists only in wild species, backcrosses will be used to transfer the trait into cultivars. Herbicide-tolerant lines will be evaluated in the field in Salinas, Central, and Imperial Valleys in the third year to demonstrate the results to the industry and seed companies, through which seeds of herbicide-tolerant cultivars will be made available to growers.